We spend a lot of time and money setting up our 4x4s with lift kits, bigger tires, winches, body armor, lights, engine and other mods, with the end goal our rigs are better equipped to handle our four-wheeling forays better than they could in stock trim. The payoff for all those efforts is our rigs look better, stand taller and run stronger, just like we’d planned. What we didn’t plan on was some of those modifications take a toll on braking, especially on older gas pickups and SUVs running vacuum-assisted brakes.

A bulkier vehicle, along with the increase in the heavier rotating mass of the tires/wheels and the change in weight transfer from a suspension lift, make it more difficult for the stock braking system to handle the job, resulting in poorer braking performance. Add a performance cam, as many of us do, and vacuum-assisted brake systems take an additional hit in braking at idle or off-throttle situations.

This degradation in overall braking performance is especially noticeable on Ford’s ’80-’96 F-150s and Broncos. Even on a good day, the vacuum-assisted brakes on these rigs feel weak and spongy when rolling to a stop or easing down a steep grade, which is common when off-roading.

Factory Ford vacuum boosters found on the ’80-’96 gas F-series and Broncos provide adequate braking power for stock applications. But when lift kits and bigger tires are added, braking performance is less than ideal—especially off-road.

Installing a cam with more lift and longer duration, as we did to our ’91 Bronco’s 5.0L, and the amount of vacuum the engine creates at idle is even less than it was stock, compounding the braking issues.

Braking Cure All

All is not lost. The cure is simple: Convert from vacuum-assist to hydraulic-assist, or “hydroboost.” Hydroboost brakes use the pressure of the hydraulic fluid in the power steering system to apply more braking force in the master cylinder, creating far more stopping power than engine vacuum could ever attain.

A great benefit of hydroboost braking power is there’s no loss in performance at idle or off-throttle situations. This is great for wheelin’ because when you ease down on a steep incline the brake pedal remains firm and the brakes rock solid. Hydroboosted brakes are also far less prone to brake fade, a common occurrence in vacuum-assisted brakes when towing in the mountains.

Those were the very reasons we decided to upgrade to hydroboost brakes on our ’91 Bronco, Eddie. We’d thought about cobbling together a hydroboost brake system using parts sourced out of a ’90s Super Duty. Then we quickly realized the fabrication, pedal alignment, and general safety issues weren’t something we were comfortable dealing with on our family daily driver.

Ruben Villalobos at Mobile Diesel Service in Oakland, Oregon, pulled the old master cylinder off our ’91 Bronco. If your master cylinder is in good shape, it can be set aside without disconnecting the brake lines.

Hydratech Conversion

After talking with Paul Clark at Hydratech Braking Systems, we opted instead to do our Ford’s brake upgrade the right way: using a hydroboost conversion kit engineered specifically for the F-series and Broncos. (Hydratech also offers a similar conversion kit for GM and Dodge trucks/SUVs running vacuum-assist brake systems.)

Hydratech uses a new OE Bosch production hydroboost unit and retrofits it with a CNC-machined T6061 billet aluminum adapter so it’s a direct bolt-in factory replacement for the big Ford vacuum booster can. The kit also includes a slick brake pedal rod and spin-on adapter that makes it easy to install and adjust brake pedal height. Hydratech also supplies two over-length Aeroquip TFE-series braided-stainless hoses and all the rebuildable/reusable AN-6 fittings to make the installation clean and tidy.

All that made it easy for Mobile Diesel Service’s Ruben Villalobos to swap out the stock vacuum-assist brake system in our truck to Hydratech’s hydroboost. It took him about two hours to make the swap, which also included replacing the old master cylinder with a new one just to make sure all was right when we hit the road.

Installed, Hydratech’s hydroboost looks far better than the big, ugly vacuum can hanging on the firewall. However, the clean look under the hood isn’t anything compared to the dramatic difference in how the brakes work and feel: the pedal is firm, the brakes aggressive. Throwing out the anchor, our big Bronco now is more like you’d expect to feel in a sports car than behind the wheel a 3-ton 4x4. The vacuum-braking woes are gone for good! We only wish the brake conversion had been addressed early on in our truck’s rebirth.

We disconnected the linkage from the brake pedal. It’s easy, just pay attention to how the brake light switch is hooked up so it goes back the same way.

Villalobos zipped off the four nuts on the cab side of the firewall that held the vacuum booster in place. He also removed the vacuum line between the plenum and the booster, and capped off the opening at the intake to prevent any leaks.

Some Ford owners cobble together a hydroboost unit from a ’90’s Super Duty (left). But its wider bolt pattern requires drilling into the bulkhead, and the brake pedal actuator is offset, requiring modifications to get brake pedal to function properly. The Hydratech unit (right) has a machined adapter plate on it. So it’s a brand new, direct bolt-in—no modifications required.

Hydratech provides a slick threaded brake-pedal link that is easily adjusted to set pedal height. Ruben made sure the locknut was tight when he had our pedal adjusted.

The Hydratech hydroboost unit slid right into place using the existing factory mounting location. We ran a light bead of RTV sealant on the back of the new booster’s CNC-machined aluminum adapter plate to ensure it had a good seal with the firewall.

Hooking up the brake pedal was a piece of cake. The actuator rod aligned perfectly, and the threaded adjustment made it easy to set the pedal height right where we liked it.

We needed a new master cylinder, so Villalobos did the required bench-bleed before it was installed on the hydroboost unit. He filled the MC with the new Type 4 brake fluid, which has better heat dissipating properties than the Type 3 of old.

Installing the new master cylinder gives us a completely new braking system. This is not the place to scrimp on reusing those old parts.

One trick we learned on making up the stainless Aeroquip brake lines is to wrap the hose 3 or 4 times with electrical tape where it will be cut to the right length using a cut-off saw. Tape keeps the wire braids from fraying.

The kit comes with a special adapter so the 90-degree AN-6 fitting can screw into the Ford power steering pump.

Hydroboost gets the added braking power by using the fluid from factory power steering pump to assist braking force instead of using engine vacuum. The Hydratech kit provided the correct fittings and hoses to make the plumbing easy.

When Villalobos finished swapping out the hoses to the power steering and steering box, the plumbing looked better than it did from the factory.

The only cutting needed was splitting the low-pressure return line from the steering box to the power steering reservoir and “T”-ing in the low-pressure return hose from the hydroboost.

Villalobos had us turn the steering wheel lock-to-lock a dozen times (with engine off) to work as much air out of the system as we could. He topped off both the brake and power steering reservoirs before we took it out for a test drive. We checked and refilled both again a few days down the road.

There was a huge difference between the marginal vacuum brakes’ efficiency prior to the Hydratech hydroboost conversion and afterwards. The swap also cleaned up the firewall.

Hydratech’s basic $565 hydroboost kit for ’80-’96 Ford F-150s/Broncos was the best safety/performance upgrade we could ever make on a truck that’s used as both a daily driver and weekend wheeler.